Test solution— Transfer a quantity of finely powdered Tablets, equivalent to about 5 mg of pentazocine and 130 mg of acetaminophen, to a suitable flask, and add 5 mL of a mixture of chloroform and methanol (1:1), shake, and allow the solids to settle. Use the supernatant.

Standard solutions— Prepare a solution of USP Pentazocine RS in a mixture of chloroform and methanol (1:1) containing 1 mg per mL (Standard solution A). Using the same solvent, prepare a solution of USP Acetaminophen RS containing 26 mg per mL (Standard solution B).

Developing solvent system: a mixture of ethyl acetate, methanol, and formic acid (90:5:5).

Procedure— Evaporate the solvents in cool, circulating air. After developing and examining the spots, spray the plate with iodoplatinate reagent prepared by dissolving 300 mg of platinic chloride in 100 mL of water and adding 100 mL of potassium iodide solution (6 in 100): the chromatogram obtained with the Test solution shows two principal spots that correspond in RF values, size, and intensity of color with the spots obtained from Standard solutions A and B.

procedure for content uniformity of pentazocine and acetaminophen—

Change to read:

Mobile phase— Prepare a mixture of chloroform, methanol, and isopropylamine (96:4:0.2).

Diluent— Prepare a mixture of methanol and 0.035 N sulfuric acid (1:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Pentazocine RS in Diluent, and dilute quantitatively with the same solvent to obtain a stock solution having a known concentration of about 0.5 mg per mL. Transfer 10.0 mL of this stock solution to a 125-mL separator. Add 30 mL of water and 5 mL of sodium carbonate solution (1:10), and mix. Extract with 60 mL of chloroform, pass the chloroform layer through filter paper, collecting the filtrate in a 100-mL volumetric flask, dilute with chloroform to volume, and mix.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 25 mg of pentazocine, to a 50-mL glass-stoppered cylinder, add 50.0 mL of Diluent, and shake intermittently for about 15 minutes. Sonicate for about 2 minutes, allow the solids to settle, and transfer 10.0 mL of the supernatant to a 125-mL separator. [note—Save the remainder of the supernatant for use in the Assay for acetaminophen. Minimize the waiting period before this test is performed to prevent significant hydrolysis of acetaminophen to p-aminophenol.USP32] Add 30 mL of water and 5 mL of sodium carbonate solution (1:10) to the separator, and mix. Extract with 60 mL of chloroform, pass the chloroform layer through filter paper, collecting the filtrate in a 100-mL volumetric flask, dilute with chloroform to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm × 25-cm column that contains 10-µm packing L3. The flow rate is about 1.2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 1000 theoretical plates; the tailing factor is not more than 3.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the liquid chromatograph, record the chromatograms, and measure the responses for the pentazocine peaks. Calculate the quantity, in mg, of pentazocine (C19H27NO) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Pentazocine RS in the stock solution used to prepare the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.

Change to read:

Mobile phase and Diluent— Proceed as directed in the Assay for pentazocine.

Standard preparation— [note—Minimize the time between addition of the Diluent and injection of the Assay preparaton to prevent significant hydrolysis of acetaminophen to p-aminophenol.]USP32 Transfer about 130 mg of USP Acetaminophen RS, accurately weighed, to a 10-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix. Transfer 2.0 mL of this solution to a 200-mL volumetric flask, and dilute with ethyl acetate to volume, and mix.

Assay preparation— Transfer 2.0 mL of the supernatant reserved from the Assay for pentazocine to a 200-mL volumetric flask, dilute immediately (to minimize hydrolysis of acetaminophen to p-aminophenol)USP32 with ethyl acetate to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains 10-µm packing L3. The flow rate is about 1.4 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 1000 theoretical plates; the tailing factor is not more than 3.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the acetaminophen peak. Calculate the quantity, in mg, of acetaminophen (C8H9NO2) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Acetaminophen RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.